Habitat ranges of central Aegean islands' Oniscidea

Aim: To investigate responses of ecological specialization on area and
environmental heterogeneity using a new metric. Location: Aegean islands
(Greece) as a case study. Taxon: Terrestrial isopods as a case study.
Methods: The new metric, ‘ecorichness’, provides an estimate of an
island’s species in the specialists-generalists spectrum. Species
presences on each island are replaced with the numbers of habitats they
exploit in the study system. Values are summed for each island and
standardized by its species richness, giving the ‘ecorichness’ of each
island. A data set with terrestrial isopods from 43 Aegean islands, and
the respective description of habitats they exploit, was used as a case
study. ‘Ecorichness’ was regressed on area, habitat diversity and the
Choros model using linear and quadratic models, evaluated based on AICc. A
reduced data set, without halophiles and coastal habitats, as well as an
alternative description of habitat diversity, were also explored. The
Small Island Effect (SIE) thresholds of a path analysis approach and
piecewise continuous linear models were compared to the area of maximum
‘ecorichness’. Results: ‘Ecorichness’ response to area and habitat
heterogeneity fits best to quadratic models and peaks at an area similar
to the SIE threshold of path analysis. The different habitat diversity
description gives similar patterns. Exclusion of coastal species and
habitats is informative on processes behind the patterns. The latter are
mostly shaped by the increasing contribution of specialists in assemblages
of larger islands. Main conclusions: ‘Ecorichness’ is a useful metric to
explore the role of ecological specialization in shaping community
patterns. It can be applied on different community data sets, provided
that information on habitats and habitat range exploitation by species is
available. Results from the case study are in accordance with previous
suggestions regarding the relative contribution of generalists and
specialists in small and large island communities.